1. Field of the Invention
The present invention relates to agricultural harvesters, and, more particularly, to the grain cleaning system portion following the threshing and separating system of agricultural harvesters.
2. Description of the Related Art
Combines are used to harvest agricultural crops such as corn, soybeans, wheat and other grain crops. As the combine is driven through crop fields, the combine cuts the crop, separates the desired crop from the undesired waste, stores the crop, and discards the waste.
In a typical combine, a header is mounted to the front of the combine to gather the crop and feed the crop into the combine for processing. As the combine is driven through the field, the crop material is collected by the header and deposited into a feeder housing. The crop material is then transported upwardly and into the combine by a feed elevator located within the feeder housing. The crop material then passes through a threshing and separating mechanism. In a rotary combine, the threshing and separating mechanism includes a rotor, a threshing concave, a rotor cage, and a separating grate. As crop material passes between the rotor, the threshing concave and the separating grate, the crop material is impacted and/or rubbed, thereby causing the grain to separate from the stalk material. The stalk material that is separated from the grain is commonly referred to as material other than grain (MOG). Other types of combines are also known that perform similar functions using different mechanisms.
After passing through the threshing and separating assembly, the grain and MOG are deposited onto a grain cleaning system. The grain cleaning system of a typical combine includes a plurality of adjustable cleaning sieves, often referred to as a chaffer sieve and a shoe sieve, and sometimes a pre-cleaning sieve. These sieves are typically reciprocated back and forth in opposite directions along an arcuate path. This motion has the tendency to separate the grain from the MOG. To further separate the grain from the MOG, a cleaning fan or blower is positioned so as to blow air up through the cleaning sieves. This flow of air tends to blow the MOG, which is typically lighter than grain, rearwardly and out the back of the combine. Grain, which is denser than MOG, is allowed to drop through the openings in the sieve.
The clean grain that falls through the cleaning sieves is deposited on a collection panel positioned beneath the cleaning sieves. The collection panel is angled so as to permit the grain to flow, under the influence of gravity, into an auger trough positioned along the lowermost edge of the collection panel. The auger trough is typically positioned near the forward end of the cleaning sieves and extends along the width of the sieves. The grain collected in the auger trough is then moved by an auger towards the side of the combine where it is raised by a grain elevator and deposited into a storage tank or grain tank. Other systems also exist that can utilize, for example, a loop conveyor system which eliminates the need for a conventional cross auger.
One of the issues confronting the systems described above relates to flow capacity of the system within given overall dimensions of the agricultural harvester. The direction of all of the grain and MOG through the axial threshing and separating system tends to increase the load on the cleaning system and make it more difficult to pass grain through ultimately to the grain tank. Complex systems have been proposed to provide multiple sieves and air blasts for ultimately separating the grain from MOG. However, these are generally complicated, add bulk to the overall system volume and are expensive.
Accordingly, what is needed in the art is a system that provides a more efficient extraction of the grain from the harvested crop material.